A set of 40 data items, produces a confidence interval for the population mean of $94.93<\mu <105.07$. If $\sum {x}^{2}=424375$, find the confidence level.

So the idea of confidence intervals is still rather new to me and one that isn't fully clear in my mind, would someone be able to give me some hints about solving this and explain what they are doing to solve it.

I get that the confidence interval is given by

$$\overline{x}-z\frac{\sigma}{\sqrt{n}}<\mu <\overline{x}+z\frac{\sigma}{\sqrt{n}}$$

and that $z={\mathrm{\Phi}}^{-1}(c)$ where c is the confidence level, however this is as far as my knowledge goes.